The proposed study investigates the social-psychology of bone marrow donors in terms of their background, motivation, and the consequences of the donation for their psychological adjustment. Sibling donors (N=100) will be compared to unrelated donors (N=583) who have given bone marrow to strangers through the National Marrow Donor Program (NMDP). Unrelated volunteers (N=500) who persist in the NMDP beyond the DR-matching will be compared to donors will also be studied in order (1) to provide a non-donor control and (2) to investigate family dynamics in the decision to donate. Actual donors receive questionnaires pre-donation, shortly post-donation, and a year post-donation. Unrelated volunteers, drop-outs, and their spouses receive questionnaires shortly after the NMPD requested DR-matching. A small subset (N=25) of each group will receive in-depth telephone interviews. Both pre- and post-donation we shall investigate subjects' commitment to altruism, self-image, mood, personality, and emotional well-being. The perceived decision-making process and gift-relationship with the recipient will also be explored, as well as perceived physical difficulties post-donation. This study should contribute to the study of altruism, the ethical evaluation of bone-marrow donation, the identification of factors that lead a potential donor to withdraw from the program, and the identification of particular types of donors at more emotional risk.